1. Field of the Invention
The present invention relates to a multi-spectrum image capturing device and a multi-spectrum illuminating device which are used to irradiate lights of different wavelengths for measurement of color components.
2. Description of the Related Art
Various types of illumination devices for illuminating a target to observe the targeted object surface and the like or capture its image for analysis have been proposed so far.
For example, Japanese Unexamined Patent Application Publication No. 9-218356 discloses an optical device and an illumination head in which, for the purpose of observing the surface of a target similar to a mirror surface, an illumination light introduced by first light guide means is irradiated to the target from a position close to a shooting optical axis through second light guide means having a plurality of reflecting surfaces so that the target can be observed with bright light obtained by the regular reflection light.
Also, Japanese Unexamined Patent Application Publication No. 9-270885 discloses a technique using a ring-shaped light source in an illumination optical system assembled in a calorimeter, etc. A light emitted from the ring-shaped light source is reflected by a first conical mirror surface and is further reflected by a second concave mirror surface for irradiating a target.
Bulb lamps have hitherto been widely used as light sources for such illumination purposes. Recently, light emitting diodes (LED's) have also been used gradually increasingly in some fields. The LED is superior to the bulb lamp in points of lower power consumption and longer life. Further, the LED has advantageous characteristics such as emission in a narrower wavelength band and high color reproducibility.
As one of techniques recently developed by utilizing those advantages and characteristics of the LED, there is a technique for measuring a target color.
For example, Japanese Patent No. 3218601 discloses a device in which LED lights of three primary colors are sequentially emitted and directly irradiated to an irradiated surface such that the respective colors are overlapped with each other in a central area, and the lights reflected from the irradiated surface are received by a photodiode, for example, to determine a calorimetric value based on the intensity of each reflected light.
In the LED, the quantity of light emitted from one device is small. In trying to constitute an illuminator for use in colorimetry, the quantity of emitted light has to be increased, for example, by arraying a plurality of LED's. However, if a plurality of LED's are just simply arrayed for illumination, there is a possibility that the target is unevenly illuminated. Some solution is required to avoid such a possibility.
As one technique in consideration of that problem, Japanese Unexamined Patent Application Publication No. 10-134621, for example, discloses an illuminator for illuminating a semiconductor wafer, etc. for the purpose of inspection. When illumination lights are emitted from a plurality of LED's and transmitted through a fiber bundle, fibers constituting the bundle are arranged at random so that even illumination is performed.
From the viewpoint of exactly measuring the target color, it is also required to avoid the regular reflection light from being included in the reflected light to be received.
As one technique coping with that point, Japanese Unexamined Patent Application Publication No. 11-305141, for example, discloses a macrophotographic device and an optical device in which an annular light shield for shielding a regular reflection light is disposed between light guide means for irradiating an illumination light and a target to be illuminated.
In the calorimetric device disclosed in the above-cited Japanese Patent No. 3218601, because the lights of three primary colors are directly irradiated to the irradiated surface, whether unevenness in the quantity of light occurs in the irradiated surface is optically decided depending on the light distribution characteristic of each LED and the illumination distance. To obtain a quantity of the optically even illumination light, it is required to form a light beam which has high directivity regardless of the irradiation distance. It is however difficult to achieve that light distribution characteristic with only the LED. In this situation, an irradiated area where the lights emitted from the LED's corresponding to the three primary colors are overlapped with each other is obtained just in a small area, and the measurement can be performed just in such a limited small area. Further, according to the arrangement disclosed in the above-cited Japanese Patent, a target color cannot be always exactly measured because of a possibility that the regular reflection light from the irradiated surface enters the photodiode.
Also, the illuminator disclosed in the above-cited Japanese Unexamined Patent Application Publication No. 10-134621 is improved in point of performing even illumination through the fiber bundle as described above, but still have problems as follows. Because of substantially vertically directed illumination, the regular reflection light from the irradiated surface cannot be avoided from entering a CCD camera through a microscope, and exact color measurement cannot be realized. Further, the disclosed illuminator is intended to inspect a pattern on a semiconductor wafer, etc., and therefore it has no special arrangement for colorimetry. In other words, the disclosed illuminator does not have a structure adapted for a plurality of illumination lights of different wavelengths.
In the techniques disclosed in the above-cited Japanese Unexamined Patent Application Publications No. 9-218356, No. 9-270885 and No. 11-305141, the LED is not assumed to be as the light source. Therefore, those techniques include no contrivance to eliminate unevenness in the illumination which is caused in the case of using a plurality of LED's.
In view of the above-mentioned state of the art, an object of the present invention is to provide a multi-spectrum illuminating device and a multi-spectrum image capturing device which are able to perform illumination without causing unevenness in the quantity of light on an irradiated surface.